A designation for a particular type of connector.

DB-25M Function Abbreviation\\
Pin #1 Chassis/Frame Ground GND\\
Pin #2 Transmitted Data TD\\
Pin #3 Receive Data RD\\
Pin #4 Request To Send RTS\\
Pin #5 Clear To Send CTS\\
Pin #6 Data Set Ready DSR\\
Pin #7 Signal Ground GND\\
Pin #8 Data Carrier Detect DCD or CD\\
Pin #9 Transmit + (Current Loop) TD+\\
Pin #11 Transmit - (Current Loop) TD-\\
Pin #18 Receive + (Current Loop) RD+\\
Pin #20 Data Terminal Ready DTR\\
Pin #22 Ring Indicator RI\\
Pin #25 Receive - (Current Loop) RD-\\
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